Subject: kern/18958: uvm_loan users use kernel_object-backed VM ranges
To: None <>
From: None <>
List: netbsd-bugs
Date: 11/06/2002 22:09:17
>Number:         18958
>Category:       kern
>Synopsis:       uvm_loan users use kernel_object-backed VM ranges
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Wed Nov 06 22:10:03 PST 2002
>Originator:     Jason R Thorpe
>Release:        NetBSD 1.6I
Wasabi Systems, Inc.
System: NetBSD 1.6I NetBSD 1.6I (YEAH-BABY-XP) #11: Sun Sep 29 17:42:25 PDT 2002 i386
Architecture: i386
Machine: i386
	Users of uvm_loan() tend to use uvm_km_valloc() or
	uvm_km_valloc_wait() to allocate the KVA at which
	loaned pages will be mapped.

	This is not a problem with basic functionality, but can
	cause interesting behavior in the face of other bugs, since
	a write fault will cause UVM to COW'd (overwriting the k-mapping
	with a non-k-mapping), which will cause a panic later, at some
	unrelated time.

	This was diagnosed by Chuq Silvers.

	See the audit trail of kern/18809.

	Provide a uvm_km_*alloc() routine which creates a backed-
	by-nothing mapping?